The invention relates to improvements in pressing rolls for withstanding the high nip forces in a high pressure roller press for interparticle crushing.
In particular, the present invention relates to an improved roll construction and the method of making the roll wherein unusually severe surface wear conditions exist in press nips having nip pressures which are capable of interparticle crushing. The new art of interparticle crushing has created new and unforeseen problems in generating surface wear of the rolls and in demanding improved nip draw-in capabilities. In interparticle crushing, two opposed rotatably seated rolls are separated from each other and form a draw-in nip therebetween wherein the pulverulent particles are drawn in and mutually crush each other.
What is referred to as interparticle crushing is a new art wherein individual particles of the grinding stock are drawn in and are mutually crushed in a product bed wherein the material fill is compressed between two roller surfaces with the application of an extremely high pressure as disclosed in such as patents as European Patent 0 084 383 and Schoenert U.S. Pat. No. 4,357,287. Other references and disclosures are found in the Beisner et al U.S. Pat. No. 4,703,897. In this art, the gap width and force applied between the rollers is such that a crushing fineness is attained by the particles entering the nip and mutually crushing one another and forming incipient cracks in the particle grains. This process and this equipment is a result of a new and unforeseen energy conservation with improved crushing.
The outer roll surfaces are subjected to extraordinarily high stressing from which among other things high wear results. It has been known to counter this wear on the basis of different shaping and coating of the drum surfaces exposed to wear. In European Published Application 0 361 172, various layers of different alloys are applied by welding to the base member of the roll for protection against wear. In U.S. application, Ser. No. 657,992, Filed Feb. 20, 1991, another approach has been proposed wherein with the employment of projections on the surface of the roll, the grinding material itself is retained on the roll surface to foster interparticle crushing, improve draw-in capabilities of the nip, and to improve the wear life.
An object of the invention is to provide an improved pressing roller which is capable of operating in an extremely high force nip environment with markedly reduced wear of the grinding surface as compared with rolls having constructions of the type heretofore known in the art.
A further object of the invention is to provide an improved interparticle crushing roll with a unique outer surface which provides for longer wear life and wherein the surface can be tailored to match the wear experience over the length of the roll with certain wear characteristics of a particular nip and a particular product being pressed.
A further object of the invention is to provide an improved press roll of the type for interparticle crushing wherein existing rolls can be modified or new rolls constructed to provide a roller wear surface of superior wear properties.